1. Field of the Invention
This invention relates to a method of manufacturing a tea drink and, in particular, to a method of manufacturing a tea drink having excellent aroma.
2. Description of the Related Art
Suppression of the deterioration of tea extract due to the oxidization is one of the important problems in the manufacturing process of a tea drink. In view of this problem, there have been proposed various methods for shutting off oxygen from the tea extract. For example, there has been proposed a method to perform the extraction of tea with deaerated water. However, this method is accompanied with a problem that it is unable to have the stable effects, since oxygen may be enabled to redissolve in the tea extract in the processes after the step of extraction. Additionally, there is also a problem that when oxygen is forcedly deaerated from the tea extract, the jumping effects of tea leaves will be lost.
In Japanese Patent No. 3452805, there is described another method, wherein the deaeration is performed with gaseous carbon dioxide. However, this method is accompanied with a problem that, since gaseous carbon dioxide is high in dissolubility to an aqueous solution, it is difficult to completely eliminate gaseous carbon dioxide from the tea extract. If the deaeration of gaseous carbon dioxide is insufficient, the sourness of gaseous carbon dioxide may be permitted to remain in the tea extract, thereby badly affecting the flavor of tea extract. Furthermore, this method is also accompanied with a problem that aroma is permitted to disperse from the tea extract during deaeration of the gaseous carbon dioxide, thereby weakening the inherent aroma of the tea drink.
In JP-A 2002-211676 (KOKAI), there is described a method of manufacturing drinks under a nitrogen atmosphere. However, since this method is directed to prevent oxygen from being dissolved in the tea extract, it is impossible in this method to lower the concentration of the oxygen that has been originally dissolved in the tea extract. In Japanese Patent No. 3083798 which is directed to the manufacture of dairy drinks, there is described a method of decreasing the generation of dimethyl disulfide to be created in the heating of dairy drinks, this method being featured in that the oxygen dissolved in the drinks is substituted by an inert gas such as nitrogen, thereby reducing the concentration of the dissolved oxygen to not more than 5 ppm. However, since a tea drink is very susceptible to changes in color tone and in aroma, this method of suppressing the oxidative deterioration by simply mixing nitrogen into the drinks is hardly applicable to the manufacture of a tea drink having satisfactory features.